Nervous System
Name:
3.5
Responses
to Stimuli
Objectives
At the end of this sub section students should be able to:
3.5.3
Responses in
the Human -Nervous
System
1.
Name the two main divisions of the nervous system
2.
Identify the CNS and PNS on a diagram of the body's Nervous System
3.
Say what a receptor is
4.
Say what a neuron is
5.
Identify 3 different types of neuron that vary in size and shape.
6.
Tell the difference between sensory, motor and interneurons
7.
Draw a diagram of a motor neuron to show its structure
8.
Give the function of -- cell body, dendrites, axon, myelin sheath, Schwann cell, and
neurotransmitter vesicles.
9.
Explain what an impulse is
10.
Distinguish between a dendrite and an axon
11.
Say what conduction of nerve impulses involves the movement of
12.
Say what a neurotransmitter is
13.
Say what a synapse is
14.
Say what a synaptic cleft is
15.
Explain the activation and inactivation of neurotransmitters.
16.
Explain how some drugs inhibit or prolong the activation or deactivation of neurotransmitters
17.
Distinguish between a presynaptic and a postsynaptic neuron
18.
Give the role of the 3 types of neuron – sensory, motor, interneuron.
19.
Give the position in the body of the 3 types of neurons – sensory, motor, interneuron.
20.
Name the 5 main senses and related organs
21.
Explain what interprets the information received by the sense organs
22.
Use a model/diagram of the SKIN to show how it functions as a sense organ.
23.
Use a model of the BRAIN to show its major parts in relation to function.
24.
Give the location and function of the following parts of the brain: cerebrum, hypothalamus,
pituitary gland, cerebellum, and medulla oblongata.
25.
Identify the main parts of a cross-section of the spinal cord
26.
Distinguish between white matter and grey matter
27.
Give the function of cerebrospinal fluid
28.
Give the function of the meninges
29.
Explain what meningitis is
30.
Distinguish between dorsal and ventral roots that project from the spinal cord.
31.
Name a nervous system disorder
32.
For paralysis, give 1 possible cause, prevention, and treatment.
33.
For Parkinson's disease, give 1 possible cause, prevention, and treatment.
34.
Show the location of nerve fibres and cell bodies in the Peripheral nervous system:
35.
Identify cell bodies in the CNS and in ganglia
36.
Explain what a ganglion is
37.
Explain the role, structure and mechanisms of the reflex arc/action.
38.
Use a prepared slide to identify, draw and label the main parts of a T.S. of the spinal cord.
39.
Write a brief note on paralysis or Parkinson’s disease.
40.
Describe a simple experiment to demonstrate reflex action
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Nervous System
Humans use two systems to respond to stimuli: the nervous system for fast action and the hormonal system for
slower responses.
Nervous
Electro/chemical messages
Carried in nerves
Fast acting
Short-term effect
Single target
Endocrine
Chemical messages
Carried in blood
Slow acting
Long-term effect
Many targets
The Nervous System
Nervous system
 Central NS (Brain & Spinal Cord)
 Peripheral NS (Cranial & spinal nerves)
o
o
Somatic NS (voluntary control of external
environment)
Autonomic NS (involuntary control of external
environment)
Functions:
 Detect changes in external and internal environment.
 Interpret these changes and respond in a coordinated manner.
 Store information gained by experience.
The CNS processes messages and controls our responses.
The PNS carries messages to and from the CNS.
A stimulus is a change to the environment that can cause
a response (nervous or hormonal).
Receptors are cells sensitive to a stimulus e.g. pain receptors, eye.
An effector responds to a stimulus e.g. a muscle contracts or a gland
secretes.
A nerve (nerve fibre) is a bundle of neurons (nerve cells) - both sensory and motor neurons.
Structure of neuron
Sensory (afferent) neuron
Diagram of sensory neuron
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Nervous System
Part of neuron
Dendron
Function
Dendrites
Cell body
Axon
Myelin sheath
Schwann cell
Nodes of Ranvier
Neurotransmitter swellings (synaptic
knobs)
Motor (efferent) neuron diagram
Interneuron
Sensory Neuron
Motor neuron
Interneuron

Carry impulses
from receptors e.g.
sense organs to
CNS.

Carry impulses
from CNS to
effector organs
(gland, muscle).

Connect
sensory to
motor neurons
in the CNS.

Unipolar (cell
body has 1 fibre)

Multipolar

Bipolar.

Involved in
reflex arc.
No myelin
sheath.

Found in the dorsal
root of spinal cord.


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
Found in ventral
root of spinal cord
Cell body is
outside the CNS.

Cell body inside
CNS.
Cell body is at end
of a short branch
along the length.

Cell body is at one
end.

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Nervous System
Transmission of nerve impulses:
Threshold: This is the minimum stimulus required to start a
nervous impulse.
All or Nothing Law: The size of the stimulus (provided it is above
the threshold level) has no effect on the size of the impulse.
Either a full message is carried or no message.
Refractory period: This is the length of time needed by a nerve cell
to recover before it can pass a second impulse.
Movement of impulse:
A resting neuron has negative ions in the inside and positive ions on the outside (hence a tiny voltage). For an
impulse to travel ions are pumped in and out of dendron/axon (needs energy). A wave of positive charge moves
along the inside of the dendron/axon producing the impulse.
The myelin speeds up the rate at which the impulse passes as does a wider axon. In a myelinated neuron the
charges can only move in and out at the nodes of Ranvier. The impulse jumps from node to node and is
transmitted more rapidly.
Synapse
The synapse is the space/gap between neurons (or between one neuron and an effector).
The axon of the presynaptic neuron ends in tiny swollen areas called synaptic knobs. These contain many
mitochondria and synaptic vesicles. These vesicles secrete a neurotransmitter substance (usually
acetycholine), into the synaptic cleft. This ensures that the impulse travels in one direction only into the
postsynaptic neuron. After transmitting the impulse these chemicals are quickly destroyed by the action of
enzymes (cholinesterase for acetylcholine) so as to clear the gap for the next impulse.
Diagram of synapse:
Significance of synapses
Advantages:
 Permit impulses in one direction only – neurotransmitters only present on one side of the synapse.
 Allow localisation of a response rather than a total body response (chaos!).
 Protect against over-stimulation, as they will slow down if overloaded.
 Their complicated interconnections allow for learning and memory.
 They ignore low-level stimulations – effectively removing ‘background noise’ from nervous system.
Disadvantages:
 Synapses are relatively slow and their number is often minimised by developing long axons and
dendrons.
 Allows chemicals to affect N.S. e.g. hallucinatory drugs, painkillers, anaesthetics and certain poisons.
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Nervous System
Neurotransmitters:
Acetycholine released from motor neurons, triggers muscle contraction. It has an inhibitory effect on cardiac
muscle, resulting in a decreased heart rate.
Noradrenaline, serotonin and dopamine affect mood. Their imbalance has been linked to depression, attention
deficit disorder (ADD) and psychosis (where behaviour and personality are altered e.g. schizophrenia).
Antidepressants and other mood-affecting drugs work by altering the levels of these neurotransmitters in the
brain.
Drugs - many affect transmission of impulses across synapse by increasing/decreasing the production of the
neurotransmitter or by affecting the rate of breakdown of the neurotransmitter.
 Ectasy affects nerve cells that produce serotonin. It causes the nerve cells to release all the stored
serotonin at once – this can cause damage to the axons. Serotonin regulates temp. as well as mood. If
body temp. reaches 430C (dancing) the blood starts to coagulate, and death can follow. Ectasy affects
memory too.
 Cannabis. Marijuana – a hallucinogen – (from the dried leaves) and hashish (resin from the flowers).
In low doses it is a depressant – impairs co-ordination, perception, timing and short-term memory. It
slows down motor activity and causes mild euphoria. It also causes disorientation, increased anxiety
(panic), delusions (paranoia) and hallucinations. Over time, marijuana can suppress the immune system,
impair mental functions and lower sperm and testosterone levels.
 Cocaine, interferes with the normal breakdown of dopamine. Dopamine is involved with pleasurable
feelings. If it is not broken down the synapse keeps on transmitting messages and euphoria follows. The
body reduces its production of dopamine which results in addiction as the user has to take more cocaine
to produce enough dopamine to feel ‘normal’. Body becomes tolerant to cocaine.
Central nervous system
 Brain and spinal cord – protected by skull and spine
 Hollow and filled with cerebrospinal fluid
 Surrounded by meninges (3).
 Contains grey matter (cell bodies) to make decisions and white matter (axons) to transport messages.
BRAIN
(Diagram)
Develops from neural tube of young embryo.
Protected by skull. Between the middle (fibrous) and inner (fine) meninges is a space filled with cerebrospinal
fluid. It is a shock-absorbing fluid that also allows exhange of nutrients and wastes between blood (arteries) and
brain/spinal cord. Outermost layer is very tough.
The brain contains outer grey matter and inner white matter.
It is made up of:
 Forebrain consists of the cerebrum, hypothalmus, thalamus, pituitary gland and pineal body.
 Midbrain is very small. Optic lobes control eye movements. It connects the forebrain with the
hindbrain.
 Hindbrain consists of the cerebellum and the medulla oblongata
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Nervous System
Parts of brain
Cerebrum
Thalamus
Function(s)
Made of 2 hemispheres, connected by the corpus callosum (bundle of
nerves). Controls thought, logic, will, intelligence, memory and
activities connected with sense organs (e.g. speech, vision, hearing)
plus sensory and motor control.
Right hemisphere controls the left-hand side of the body and vv. In
general the left side is dominant for hand use (RH), language, maths
and logic. The right side specialises in art, music, shape recognition
and emotional responses.
It receives all the messages from the senses and directs them to the
correct place in the cerebrum. Controls emotional state e.g. pain,
pleasure.
Hypothalmus
Regulates the internal environment (homeostasis) by monitoring
osmoregulation, appetite, thirst, body temp., heart rate, sleep, blood
pressure, breathing, peristalsis, aggression and sexual activity. Assists
hormonal function of pituitary.
Pituitary
Pineal body
Olfactory lobes
Cerebellum
Medulla
oblongata
Master hormone gland. Controlled by hypothalamus.
Controls sleep/wake cycles
Concerned with sense of smell
Controls balance and muscular co-ordination. Affected by alcohol.
Smallest part of brain, situated where spinal cord enters brain.
Controls involuntary muscles such as those involved in breathing
(diaphragm), heart rate, swallowing (peristalsis), coughing, salivating,
blood pressure, vomiting and sneezing. Detects levels of carbon
dioxide in blood.
Relays info. between cerebrum and cerebellum
Pons
Functions of cerebrum
(diagram)
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Nervous System
SPINAL CORD
Transmits impulses to and from brain and controls many reflex actions. The spinal cord has an inner grey
matter and outer white matter with 31 pairs of spinal nerves.
Reflex Action
*A reflex action is an automatic response to a stimulus, which is not
controlled by the brain.
*A reflex arc is the nerve pathway involved in a reflex action.
Reflex arc consists of:
receptor → sensory neuron→ spinal cord → intermediate neuron (sometimes)
effector e.g. muscle/gland
→ motor neuron →
At the interneuron stage an impulse is sent to the brain to make it aware of the action but the brain does not
control it.
Knee jerk diagram
The patellar tendon is stretched by a sharp tap. Stretch receptors in muscle are stimulated. An impulse is sent to
spinal cord in waist via the sensory neuron. This synapses with the motor neuron and an impulse is sent to the
motor end plate and stimulates the extensor muscle in leg to contract and leg jerks out.
Finger burn
Heat receptors in skin → sensory neuron → CNS
(biceps contract)
→
Intermediate neuron → motor neuron → effector
Significance of simple reflex actions:
Besides being automatic responses (do not need to be learned) these reflexes are fast and protect the body from
injury.
Other examples of simple reflex actions include control of pupil size, eye blink, accomodation in the eye,
swallowing, coughing, salivating & grasp reflex in children.
Conditioned reflexes are altered reflexes. They involve a form of learning e.g. increased salivation on hearing
the clatter of dinner plates.
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Nervous System
Nervous system disorders (learn one)
Parkinson’s disease
is a progressive neurological disorder that affects the control of voluntary movement.
 Cause:
Cause unknown but stems from a deficiency of dopamine, due to loss or damage of tissue in the brain that
makes dopamine. Dopamine is used to regulate the nerves controlling muscle activity.

Symptoms:
Tremor of hands and/or legs, muscle rigidity and slowness of movement. This results in stooped posture,
drooling of saliva, shuffling walk.
 Treatment:
No cure currently. Symptoms can be reduced by the drug levodopa (L-dopa), which the body converts into
dopamine. Long-term use of these drugs can give many unwanted side-effects (including vomiting, nausea,
hallucinations and uncommanded movements). Some experiments have been done in transplanting foetal
dopamine-producing tissue into patients. Results variable.
Paralysis
 Cause:
Include blood clot, resulting a stroke, spinal injury from a road accident, sport etc., polio, muscular dystrophy (a
genetic disease).
 Symptoms:
Paralysis results in a person not been able to use some or all of their muscles or use all their senses. A protein
that prevents growth surrounds neurons, which run up and down the white matter of the spinal cord. Damage to
these neurons cannot be repaired in the normal way. Crushing or severing of the spinal cord will lead to loss of
function of nerves lower down the cord.
 Treatment
No cure. Some work has been carried out in animals by bridging gaps with neurons or splicing broken neurons
through grey matter, which allows growth.
 Prevention
Reduce further damage to spine when moving accident victims by immobilising neck and head.
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Nervous System
Nervous System Examination Questions
1. [2006 OL] [Q15(c)(iii)]
Name the part of the central nervous system that runs through the vertebrae.
2. [2007 OL ]
[Q15(a)]
The diagram shows part of a reflex arc.
(ii)
(i) Name neurons A, B and C.
In which direction is the impulse transmitted A  B  C or C  B  A ?
(ii) Name the small gaps between neurons.
(iii) Neurons produce neurotransmitter substances. What is their function?
(iv) Give an example of a reflex action in humans.
(v) Why are reflex actions important in humans?
3. [OL 2011] [Q14(b)]
The central nervous system is made up of two main parts.
Name each part.
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Nervous System
Name a disorder of the nervous system.
Give one cause of the disorder and suggest a means of treating the disorder.
4. [OL 2012] [Q15(b)]
In relation to animal responses:
Name the two main parts of the central nervous system in humans. Messages are carried around the body by
neurons (nerve cells).
Name any two types of neuron.
What name is given to the area where one neuron ends and another begins?
Name the type of chemical that carries messages between two neurons.
What happens to this chemical once the messages have been transmitted?
5. [2004 HL]
[Q15(a)]
(i) Draw and label sufficient of two neurons to show a synaptic cleft.
(ii) Describe the sequence of events that allows an impulse to be transmitted across a synapse from one
neuron to the next.
(iii) Suggest a possible role for a drug in relation to the events that you have outlined in (ii).
6. [2005 HL] [Q3(b)]
Indicate whether the following are true (T) or false (F) by drawing a circle around T or F.
Motor neurons conduct impulses towards the central nervous system.
T
F
7. [2005 HL] {Q14(c) (iii)]
Name a disorder other than cancer for each of the following and indicate a possible cause
and a means of treatment:
Nervous system.
8. [2006 HL]
[Q14(b)]
(i)
What is a neuron?
(ii)
Distinguish between sensory, motor and interneurons (association neurons).
(iii)
Briefly explain the role of neurotransmitter substances.
(iv)
State a function for 1. Schwann cells, 2. Myelin sheath.
(v)
In relation to Parkinson’s disease or paralysis give:
1.
A possible cause,
2.
A method of treatment.
9. [2008 HL]
[Q4]
The diagram shows a motor neuron.
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Nervous System
(a)
Identify parts A, B and C.
A…………………………… B ……………………………… C……………………………..
(b)
Give a function of A …………..………………………………………………………………….
……………………………………………………………………………………………………
(c)
Place an arrow on the diagram to show the direction of the impulse.
(d)
Give a function of C ……………………………………………………………………………..
……………………………………………………………………………………………………
(e)
Place an X on the diagram at a point at which a neurotransmitter substance is secreted.
(f)
What is the role of the motor neuron? …………………………………………………………..
10. [2010 HL]
[Q11(a)(b)]
(a) (i) Name a disorder of the human nervous system.
(ii)
In the case of the disorder referred to in part (i) state:
1. A possible cause.
2. A means of prevention or a treatment.
(b)
(i)
(9)
1.
What is a reflex action?
Give one example of a reflex action.
Suggest an advantage of reflex actions.
The parts of the nervous system involved in a reflex action make up a reflex arc.
Draw a large labelled diagram to show the structures involved in a reflex arc.
2.
Place arrows on your diagram to show the direction of impulse transmission in the reflex arc.
(ii)
(iii)
(iv)
11. [2011 HL] [Q11(a)]
Name a disorder of the human nervous system. State:
A possible cause.
A means of prevention or a treatment.
12. [HL 2012] [Q13]
(a)
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Nervous System
(i) Distinguish between the central nervous system and the peripheral nervous system. Include a clear reference to each in
your answer.
(ii) Give one way in which a nervous response differs from a hormonal response.
(b) (i) Draw a large labelled diagram of a motor neuron.
(ii) Give one function each of any two parts found only in neurons.
(iii) Place an arrow on or near your diagram to indicate the direction of impulse transmission. (iv) Name and
state the role of any two types of neuron, other than the motor neuron.
(c) (i) State one function for each of the following parts of the human brain.
Cerebrum; Hypothalamus; Cerebellum; Medulla oblongata.
(ii) In relation to the nervous system, distinguish between grey matter and white matter. Include a clear reference
to each in your answer.
(iii) In the case of either paralysis or Parkinson’s disease state:
1. a possible cause, other than accident;
2. a method of treatment.
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Nervous System
Marking Scheme – to be updated
1. [2007 OL ]
[Q15(a)]
(i) sensory or receptor/ inter-or relay or connector/ motor or effector
(ii) A B C
(iii)
synaptic cleft or synapse
(iv)
to carry impulse/ across gap
(v) example of action
example of reaction
(vi)
fast response or defence against injury
2. [2004 HL]
(i)
[Q15(a)]
Diagram of synaptic cleft: 6, 3, 0
3 labels 3(2)
(ii) Transmission of impulse: arrival of impulse / synaptic bulbs (or vesicles) /
(secretes) transmitter (substance) / passage of neurotransmitter /
impulse starts in next neuron / neurotransmitter broken down / by enzymes
any five 5(3)
(iii)
A drug may be used to inhibit or enhance transmission of impulse or
similar comment
[any reasonable suggestion] 3
3. [2005 HL] [Q(3b)]
False
4.
[2006 HL]
[Q14(b)]
(i)
nerve cell 3
(ii) sensory: towards CNS or named part or from receptor or
structural feature 3
motor: away from CNS or named part or to effector or
structural feature 3
inter: links two neurons 3
(iii)
carries impulse / across synaptic cleft /
triggers impulse in next neuron any two 2(3)
(iv)
Schwann cell: produces myelin (sheath) 3
Myelin sheath: insulation or protection or speeds impulse 3
(v) Disorder:
Cause: injury / genetic / disease / lack of dopamine / 3
Treatment: physiotherapy / stem cell / dopamine or
drugs qualified 3
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Nervous System
5. [2008 HL]
[Q4]
(a) A = myelin sheath or Schwann cell B = myelin sheath or axon
C = dendrite3(1)
(b) A: (myelin sheath) insulates or protection or speeds up impulse (message)
A: (schwann cell) produces myelin (or sheath) or insulates or protection or
speeds up impulse (message) 3
(c) arrow (right to left) or from dendrites towards cell body 3
(d) receives impulse or carries impulse (message) to cell body 3
(e) X on terminal dendrites on left 3
(f) receive or carry impulse (message) and to muscle or gland or effector or
from CNS 5, 0
6. [2010 HL]
[Q11(a)(b)]
(i) Paralysis or Parkinson’s . . . 3
(ii) 1. Relevant cause3
2. Relevant means of prevention or treatment3
(b) (i) automatic / response to a stimulus / involuntary (or not controlled by brain)
Any two 2(3)
(ii) e.g. coughing, blinking, sneezing etc. 3
(iii) Protection or fast (response) 3
(iv) 1. Diagram
(sensory neuron, motor neuron, spinal cord and correct position of
cell bodies for 6 marks) 6, 3, 0
Labels:
receptor (or named), sensory neuron, inter neuron,
motor neuron, cell body, effector (or named) Any
three 3(2)
2. Arrow in (dorsal) + arrow out (ventral) 3
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